1. Field of the Invention
The present invention relates to a heat dissipating fan, and more particularly to a heat dissipating fan with an oil guide for a lubricating bushing.
2. Description of Related Art
With reference to FIG. 5, a conventional heat dissipation fan in accordance with the prior art comprises a casing (50), a stator (60), a lubricating bushing (70) and a fan (80). The fan (80) is rotatably mounted in the casing (50). The stator (60) with an electromagnet and a circuit board (62) is securely mounted in the casing (50). A permanent magnet (not numbered) is mounted in the fan (80) to be a rotor, such that the fan (80) can rotate due to the interaction between the magnetic forces in stator (60) and the permanent magnet. A sleeve (61) pressed into the stator (60) is engaged with an annular groove (53) defined around a base (52) formed in the casing (50). A lubricating bushing (70) has a lubricant impregnated in the material forming the lubricating bushing (70). The lubricating bushing (70) is pressed into the sleeve (61). A shaft (81) extends from the fan (80) and through a passage (71) defined through the bushing (70). A locking disk (63) is mounted in a neck (82) defined near the free end of the shaft (81) to securely hold the shaft (81) in the bushing (70). Accordingly, the fan (80) can rotate relative to the casing (50) with very little friction. A cavity (521) is defined in the top of the base (52), such that a chamber is defined in the base to hold the lubricant oil from the lubricating bushing (70) as the dissipation fan is operated.
To assemble the conventional heat dissipation fan, the locking disk (63) is put on the base (52) and covers the cavity (521). The shaft (81) aligns with the passage (71) in the bushing (70), the bushing (70) aligns with the sleeve (61) and the sleeve (61) aligns with the annular groove (53) around the base (52). The fan (80) is then pressed with a press machine. The shaft (81) will extend through the passage (71) in the bushing (70) and engage with the locking disk (63), the bushing (70) is pressed into the sleeve (61) and the sleeve (61) is pressed into the annular groove (53). Consequently, the assembly of the conventional dissipation fan is completed.
However, during the assembly of the conventional heat dissipation fan, the air contained in the cavity (521) cannot be released and high pressure will build up in the chamber. The high pressure will resist the assembly of the dissipation fan. In addition, the lubricant easily flows out due to the pressure in the chamber, so the bushing (70) will easily dry out. The useful life of the heat dissipation fan is decreased.
To overcome the shortcomings, the present invention provides an improved heat dissipation fan to mitigate or obviate the aforementioned problems.
The main objective of the invention is to provide an improved heat dissipation fan with an oil guide. The dissipation fan has a casing, a stator, a lubricating bushing and a fan. The casing has a base with a cavity defined in the top of the base. A sleeve is pressed onto to the base, and the stator is pressed onto the sleeve so as to be attached to the base. Lubricant is impregnated in the material used to form the bushing, and the lubricating bushing is mounted in the sleeve. The fan is rotatably mounted in the casing and has a permanent magnet as a rotor. A shaft extends from the fan and through a passage defined through the lubricating bushing. A locking disk is securely mounted on a free end of the shaft to lock the shaft in the lubricating bushing. An oil guide is formed on the lubricating bushing through which the lubricant recycles during the operation of the dissipation fan. With such an arrangement, the build up of the air pressure in the cavity during the assembly of the dissipation fan is released through the oil guide. A pressure balance between the cavity and the environment is achieved. The oil guide can keep oil from flowing out of the sleeve and drying out the lubricating bushing. The useful life of the dissipation fan is prolonged.